Retinitis pigmentosa is a hereditary retinal degeneration that leads to loss of night vision, side vision, and eventually most of central vision. Cystoid macular edema (CME), a complication involving swelling of the central retina and reduction in visual acuity, occurs in at least 25% of patients with retinitis pigmentosa, often before their central vision has become impaired due to the primary disease process. Some patients with retinitis pigmentosa have CME that is poorly responsive to treatment with eye drops or injections into the eye, while other patients may show a reduction in swelling with only an incomplete recovery of visual acuity following treatment. Iodine supplementation has been suggested as a way to reduce edema in different tissues. We have evidence that taking an iodine supplement reduces the risk for CME in patients with retinitis pigmentosa. Since an iodine supplement may constitute only a small fraction of total dietary intake of iodine, the main purpose of the present study is to determine whether the likelihood of having CME in retinitis pigmentosa is related to iodine concentration in the urine, as a measure of the total dietary iodine intake. Since gamma linolenic acid (GLA) has also been suggested as a way to reduce edema, we will determine whether the risk of CME is inversely related to dietary GLA as a secondary goal. To address these issues, we will use optical coherence tomography to detect CME, quantify urinary iodine concentration as a measure of total dietary iodine intake, and measure GLA intake based on food frequency questionnaires in 200 patients with retinitis pigmentosa. If the risk of CME is found to be inversely related to urinary iodine concentration and/or GLA intake in this population, then a clinical trial could be considered to determine whether higher dietary iodine and/or GLA intake will help protect patients with retinitis pigmentosa from developing CME or, possibly, reduce CME in those who already have it.